Process for soap coating of metals



Patented Oct. 10, 1944 UNITED STATE mocass ron soar COATING 011 METALS Robert W. Shoemaker, Anderson, Ind., -assig nor to Agnes J. Reeves Greer, Morgantown, W. Va.

No Drawing.

Application January 27, 1943, Serial No. 473,753

L 20mm. (01. 117-134) 1 The invention relates to the treatment of.

metals, such as the cleaning, neutralizing and protective coating of pickled metal, and particularly to the provision of a protective film upon the cleaned surface of the metal to prevent corrosion of the metal by contact with moisture, and the present invention is an improvement upon my prior Letters Patent No. 2,257,133, dated September 30, 1941.

In said prior patent I disclosed and claimed a process for removing the pickling acid from the surface of metal and applying a protective coating to .the cleaned surface to prevent corrosion. That process consisted in removing virtually all traces of acid from the surfaces and pores of the metal with an alkaline solution which also contained ordinary soap and a wetting agent for facilitating the action of the alkali in rapidly. -cleansing the surface and pores of the metal, after which the cleaned metal was coated with a protective film of alkali and a polyhydric alcohol such as glycerine or glycol.

The addition of a foam eliminating agent, a

"precipitating agent and a bleaching agent was optional in either or both of the solutions in cases where one or more of such results might be desired.

The invention as disclosed in my prior patent has been practiced commercially for some time with very satisfactory results, and coils of pickled metal strips, protected with a film of alkali and glycerine have been kept entirely free of corrothe metal from rust or oxidation for a few weeks.

It is therefore an object of the invention to provide a process for protecting metal from oxidation by applying a protective film of ordinary soap to the cleaned surfaces of the metal.

Another object is to provide a process for treating pickled metal which consists in removin acid from the surface of the metal by a solution containing alkali and immediately coating the cleaned surface of the metal with a solution containing ordinary soap. Still another object is to provide such a proces in which the pickling acid is removed from the surface of the metal by a solution containing alkali and the cleaned surface is-then coated with ordinary soap and a, wetting agent. A further object of the invention is to provide for cleaning the surface of pickled metal and protecting it against corrosion by submerging the metal in a solution containing caustic alkali and ordinary soap.

the cleaned surface of the metal is covered by a protective film of soap, which protects the metal against oxidation for a period of several weeks.

Thus the ordinary soap acts not only as a cleanser to speed up the action of the alkali in removing traces of acid from the metal but it also functions as a protective coating or film upon the surface of the metal to protect it against rust for a limited period of time.

I have also discovered that where the metal is thoroughly cleaned, either by washing in a solution such as contained in the first washing tank in my prior Patent No. 2,257,133, above referred to, or by thoroughly washing in clear water, or by shot.blasting, or the like, so that all scale and oxidation is removed from the surfaces of the metal, a protective film or coating of ordinary soap applied to the surfaces of the metal, prompt- 1y after the cleaning of the same, will protect Still another object is to provide a process for cleaning the surface of pickled metal and forming a protective coating thereon by submerging the metal in a'solution containing caustic alkali,

a wetting agent and ordinary soap.

The above objects may be attained by carrying out the improved process in the manner hereinafter set forth in detail.

The invention is being practiced commercially in a pickling machine such as disclosed in Greer Patent No. 2,091,921, dated August 31, 1937, but it should be understood that the invention may be practiced in any other form of continuous pickling machine or in any conventional arrangement of pickling and washing tanks. I

In its broadest concept, the invention consists in the coating of a metal surface with a protective film of ordinary soap to prevent rusting or corrosion thereof for a limited time after the treatment.

The surface to be treated with the protective coating should of course be cleaned to remove any oxidation or rust before the protective film is applied thereto. This cleansing maybe accomplished by the use of a solution such as disclosed in the first washing tank, in my prior patent above referred to, or the metal may be washed in clear cold water, especially where a thorough rinsing in running water is provided,

as in the case of the large continuous strip the surfaces of the metal. This may be accomplished by submerging the metal in a solution containing ordinary soap, or the solution may be sprayed upon the surfaces of the metal or otherwise applied thereto.

This soap solution is preferably hot in order to obtain the most desirable results, very desirable results having been obtained by maintaining the solution at a temperature of from 140 F.

, to 212 F.-, although the solution may be cold in cases where it is not possible or practical to keep the same heated.

Other ingredients, such as caustic alkali, a wetting agent, a precipitating agent, and in some cases a bleaching agent may be added to the solutions, in proportions as hereinafter specified,

but it has been found in practice that very good.

results may be obtained by using only soap and water.

The soap may be any ordinary soap, preferably in the form of soap powder or chips, very good results having been achieved with soap chips sold under the name of Ozonite.

The proportion of soap used in the solution may be varied, the amount of soap usually being from about twenty-five pounds to one hundred pounds in a tank containing about forty-eight hundred gallons of water. Very good results have been obtained by using about seventy-five pounds of ordinary soap in this amount of water without the addition of any other ingredients, the metal so treated having remained clean and bright without any signs of rust for many days after the treatment.

Excellent results have also been obtained by coating the surfaces of the metal with a solution containing ordinary soap and caustic alkali,

using about seventy-five pounds of soap and fifteen or twenty pounds of caustic alkali in a forty-eight hundred gallon tank of water, preferably hot. The proportion of caustic alkali may be varied, a range of five pounds to thirty pounds of alkali having proven very satisfactory.

The caustic alkali used may be caustic soda or any one or combination of several prepared compounds containing sodium carbonate, sodium hydroxide, sodium cyanide and the like and known to the trade as Orthosil, Cyanegg and Super Alkali No. 4.

In practicing the invention in connection with the pickling ofmetal, the three conventional tanks, common to all pickling machines and pickling processes, may be used, the pickling operation being performed in the first tank, the cleansing of the metal being carried out. in the second tank and the protective coating or film being applied in the third tank.

Any usual practice of pickling the metal may be carried out in the pickling bath, the present invention being concerned only with the other two tanks which are hereinafter referred to as the first and second washing tanks.

As above stated, the first washing tank may contain only water, especially in the case of a continuous strip pickling machine where the tank is of great length and running water is continuously passed therethrough.

However, in pickling machines or processes where such large tanks are not used, the cleaning of the metal may be speeded up by adding one or more ingredients to the water in the contain caustic alkali for neutralizing the pickling acid remaining-upon the metal. It is known that if any free acid remains upon the metal this will cause the metal to rust when exposed to the moisture of the air even though a protective coating of oil or the like be immediately placed upon the surface of the metal. Therefore sumcient alkali may be used to not only neutralize the acid but to act as an inhibiter to prevent concentration of free hydrogen ions to decompose or rust the metal for sometime after it has been removed from the solution.

For the purpose of carrying the alkali into the pores of the metal and to more rapidly and thoroughly cleanse the entire surface and pores of the metal, an ordinary soap or a wetting agent, preferably both, may be added to the alkaline solution in the first washing tank. Any ordinary soap powder or soap chips which are effective in alkaline solution, such as the Ozonite soap chips above referred to, may be used for the purpose.

Only a relatively small quantity of ordinary soap or wetting agent is necessary to give very satisfactory results, and although I do not intend to limit the invention to such exact amounts I have found that where both ordinary soap and a wetting agent are used together in the alkaline solution, the soap powder or soap chips may be used in proportion ranging from 125% to 275%,

and in actual practice with a first washing tank containing about 5600 gallons of water, 5 to 20 pounds of ordinary soap powder or soap chips have been found sufilcient.

This ordinary soap not only assists in cleansing 40 hibit rusting.

The caustic alkali used in this first washing tank may be either caustic soda or a prepared compound such as above mentioned, and maybe in amounts ranging from .275% to 550% although as above stated I do not wish to be limited to the exact proportions.

Very satisfactory results are being obtained by using from 40 to pounds of'caustic soda in this first washing tank, or by using from 75 pounds to 225 pounds of one of said prepared neutralizing agents, as a substitute for the caustic soda.

A small quantity of a wetting agent may be used in this tank and is preferably used in combination with the ordinary soap as it causes the caustic alkali and the soap to more quickly enter the pores of the metal, neutralizing the acid therein and more thoroughly and rapidly cleans-.

ing the metal.

This wetting agent may be one of the so-called soapless soaps and the amount used may be varied although in actual practice it has been found that from .02% to .5% of the same is sufficient when used with the above mentioned amounts of alkali and of the soap. I

Such wetting agents are used because their high penetrating qualities very materially reduce the surface tension of the water so as to allow complete, rapid penetration of the pores of the metal by the alkali and soap. 1

In order to prevent foaming of the solutio the wetting agent maybe also a foam eliminating agent such as sodium metaphosphate, or sodium hexametaphosphate, which may be Oh! tallied commercially under the name of calgon.

From to gallons of this wetting agent added to the solution in the first washing given very good results.

The wetting agent may be a sodium salt of sulphated alcohol obtained from coconut oil, such as may be obtained commercially under the name of Orvus W. A. paste, in which case preferably 10 to 20 pounds of the same is used in the first washing tank, or other commercial products which will materially reduce the surface tension of the water may be used.

Such wetting agents will not form any insoluble lime soaps when used with hard water and are eflective in alkaline or acid media.

If it is found necessary or desirable to precipitate suspended or colloidal particles in this solution a small amount, approximately .002% to .006% of a suitable chemical may be used.

Good results have been obtained by using 1 to 3 pounds of a mixture of ground sulphate of .aluminum, sodium carbonate and sodium bicarbonate, which mixture may be obtained commercially under'the name of The Old Settler.

For the purpose of giving the steel a whiter color, small amounts of a bleaching agent have been used in some instances. Sodium hypochloride may be used in quantities of .01% to .04%; l to 2 gallons of this bleaching agent in the first washing tank having given the metal a whiter color in actual use.

However, due to the fact that this bleaching agent is to some extent an oxidizing agent its use is not recommended where the steel is to be kept for any length of time before cold rolling or other processing, and since the bleaching agent is only used for giving a whiter color to the steel and is not otherwise necessary in the presentprocess, it may be eliminated without afiecting the process.

Although the best results are obtained by using hot water as above described in the first washing tank, it should be understood that even with the use of cold water the above solution is very effective in thoroughly and quickly cleansing the pores and surfaces of the metal.

tank have ond washing tank for the purpose of driving the film of alkali and soap into the pores of the metal. This wetting agent may be used in substantially the same proportions as in the first washing tank and in practice from 5 to pounds of Orvus W. A. paste or from 5 tom gallons of Calgon have given very good results.

In order to precipitate suspended or colloidal particles in the, solution of the second washing tank a small amount of a suitable precipitating agent may be used. From .002% -to .006% of a suitable chemical may be used for this purpose. In actual practice from one to three pounds of the commercial product, sold under the name of The Old Settler, have been used with very satisfactory results. As above stated this product is a mixture of ground sulphate of aluminum, sodium carbonate and sodium bicarbonate. v

In some cases a small amount of bleaching agent, such as sodium hypochloride, preferably about .025% to .05% may be added to the solution in the second tank; although as above stated in reference to the first washing tank, this bleaching agent may be eliminated without affecting the process.

The protective quality of the film or coating of ordinary soap alone or in combination with caustic alkali has been found to be suflicient to prevent rusting of the metal for a substantial time, So that if the metal is to be cold rolled, or otherwise worked, that is within a few weeks after the tained in solution in one tank, orseveral tanks After the neutralizing and cleaning has been carried out in the first washing tank as above described, the metal is preferably transferred immediately to the second washing tank where the protective coating may be applied thereto.

Although cold water may be used in this second washing tank, I prefer to use hot water which may be maintained at a temperature of from 140 to 212 F. As above stated, this tank may contain only soap and water. However in some cases it has been found beneficial to add caustic alkali to the solution, and other ingredients may be added in the amounts given below. The proportion of caustic alkali used in this tank may be from .01% to .55%. In actual use in practicing the invention this second tank was of somewhat smaller capacity than the first tank and contained about 4800 gallons in which amounts of caustic soda varying from 5 pounds to 30 pounds have given very satisfactory results. The proportion of ordinary soap, preferably in the form of soap powder or chips, used in this second tank may be substantially the same as in th first washing tank but is preferably considerably increased in order to form a protective film V or coating oi soap upon the surface of the metal, twenty-five to one hundred pounds of soap giving very satisfactory results.

If desired a small amount of any of the wetting agents above referred to may be-used in the secmay be used, each containing a solution of one or more of the above named ingredients, and the following claims should be read with this understanding.

I claim:

I. The method of treating metal to prevent corrosion which consists in cleaning the surfaces of the metal, then coating the clean surfaces of the metal with a. film of a solution consisting of ordinary'soap a precipitating agent consisting of a mixture of sulphate of aluminum, sodium carbonate and sodium bicarbonate and a wetting agent taken from a group consisting of sodium metaphosphate, sodium hexametaphcsphate and sodium salt of sulphated alcohol obtained from coconut oil, and then removing the metal from the solution and drying it to form a protective film upon the surfaces of the metal.

2. The method of treating pickled metal directly after the pickling thereof to neutralize the adhering acid and inhibit rusting of the metal which consists in rinsing it in a solution containtating agent consisting of a mixture of sulphate of aluminum, sodium carbonate and sodium bicarbonate and a wetting agent taken from a group consisting of sodium ,metaphosphate, sodium hexametaphosphate and .sodium saltof sulphated alcohol obtained from coconut oil, and then removing the metal from the solution and drying it to form a protective coating upon the surfaces of the metal.-

ROBERT W. SHO. 

